One or more embodiments of the subject matter described herein relate to over current protection devices for electric circuits.
Known electric circuits include a power source that delivers alternating or direct current to an electric load through one or more conductive busses. The current may temporarily and abruptly increase, or “spike,” which can cause significant increases in the energy of the current that is transmitted to the load. The variances or spikes in the current may be referred to as an overcurrent, or an overcurrent event. Overcurrent events can damage the load that is powered by the current. For example, the load may include relatively sensitive electronic components that are damaged or destroyed by overcurrents of significantly high energy. Alternatively, the overcurrent events can risk injuring operators of the load.
In order to protect loads from such overcurrents, some known circuits include overcurrent protection devices, such as fuses and contactors, that protect the load and/or operators from overcurrents. The fuses have an energy threshold value that dictates when the fuses fail, or “blow.” For example, when the energy of the current in an overcurrent exceeds the energy threshold value of a fuse, the fuse may blow and open the circuit to prevent additional current from flowing to the load. One problem with relying on the energy threshold value of a fuse to protect the load and/or operators of the load is that the energy threshold value may be dependent on external factors, such as the temperature and/or age of the fuse. The fuse may unnecessarily blow at overcurrents having energies that are low enough for the load and/or operators of the load to safely withstand. Additionally, the fuse may be located in a relatively difficult location to reach. As a result, in order to replace the blown fuse, significant downtime of the circuit and load may be required.
Some known contactors operate by opening the circuit when the current exceeds a threshold of the contactor for a predetermined time period. Once the current exceeds the threshold for the time period, the contactor opens to prevent additional current from flowing to the load. One problem with some known contactors is that the contactors have a response time or delay between receiving instructions to open the circuit and actually opening the circuit. During this delay, some current may flow through the contactor to the load and/or fuses located between the contactor and the fuse. This current has energy referred to as “let-through fault energy.” The let-through fault energy can degrade fuses that are coupled with the circuit and/or damage or injure the load and operators of the load.
A need exists for an improved electric circuit protection system and method for protecting electric circuits.